Single Dockerfile for building ATAT.

Dockerfile is now a single multi-stage build that relies on a Python 3.7
base image.

Notes:
- This builds uWSGI with a `pip install` because the Alpine vendored
  uWSGI is built against Python 3.6.
- Adds a docker-compose file that can be used for testing that the build
  works. It is not usable for development purposes because it creates a
  static copy of the application.

deploy/docker/sample.nginx.conf

@@ -0,0 +1,24 @@
+server {
+    listen       80;
+    server_name  localhost;
+
+    #charset koi8-r;
+    #access_log  /var/log/nginx/host.access.log  main;
+
+    location / {
+        try_files $uri @app;
+    }
+
+    location @app {
+        include uwsgi_params;
+        uwsgi_pass unix:///var/run/uwsgi/uwsgi.socket;
+        uwsgi_param HTTP_X_SSL_CLIENT_VERIFY $ssl_client_verify;
+        uwsgi_param HTTP_X_SSL_CLIENT_CERT $ssl_client_raw_cert;
+        uwsgi_param HTTP_X_SSL_CLIENT_S_DN $ssl_client_s_dn;
+        uwsgi_param HTTP_X_SSL_CLIENT_S_DN_LEGACY $ssl_client_s_dn_legacy;
+        uwsgi_param HTTP_X_SSL_CLIENT_I_DN $ssl_client_i_dn;
+        uwsgi_param HTTP_X_SSL_CLIENT_I_DN_LEGACY $ssl_client_i_dn_legacy;
+        uwsgi_param HTTP_X_REQUEST_ID $request_id;
+    }
+}
+